The one prior art tension alert tool has one end being an opening head. Another end of the driving portion is formed as a buckling unit. The buckling unit is formed by an upper teethed block and a lower teethed block. The upper teethed block is engageable to and bidirectionally moveable through the lower teethed block. An elastic unit encloses the driving portion and is installed above the buckling unit. The elastic unit is a spring. The handle is formed with a receiving groove for receiving the buckling unit and the elastic unit of the driving portion. The buckling unit will compress the elastic unit.
In operation, when the opener of the present invention is used to screw an object so that the driving portion rotates and the elastic unit rotates therewith. When the twisting force to the screw unit has achieved to an upper limit value, the elastic unit will release the engagement of the upper teethed block and lower teethed block so that the upper teethed block will move through the lower teethed block. The user determines whether the tension applied to a screw unit is overlarge by hearing the collision voice between the upper teethed block and lower teethed block so as to determine whether it is necessary to stop the operation.
However in this prior art, the sense of the over tension is determined by the touch feeling of the user, if the user has no precise touch feeling, he (or she) can not find that the applied tension is too large and is necessary to stop of the operation, as a result, an overlarge force is applied so as to destroy the structure and engagement of the upper teethed block and lower teethed block. For a long time, the setting value of the tension will change so as to lose the precision in operation.
Furthermore, in the prior art, the worker determines the over tension state by hearing the collision between the upper teethed block and lower teethed block, however in a noisy environment, it is often that the user can not hear the voice of collision.